GDK/Win32: Force GLES if running on ARM64

Hi,

This MR is open to force running GL in OpenGL/ES 3 on Windows on ARM (i.e. Windows 10 on ARM64), if building for OpenGL/ES using libANGLE is enabled as:

-In emulated x86 mode, the system provides only up to OpenGL 1.1, which is not enough for our use case, and ARM64 graphics drivers do not provide more advanced GL features.

-In native ARM64, there is even no a rudimentary Open#1 (closed).1 opengl32.dll provided. This, however, likely means that we need to update the build files for libepoxy at one point that we should skip building for WGL when we are building for Windows on ARM (update: I was able to build libepoxy on ARM64 Windows out-of-the-box, but obviously the WGL tests are going to fail, since OpenGL is more or less a stub on ARM64 Windows).

With blessings, thank you!